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repeater squeal

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Ramchops

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I was curious about something and thought yall can help. When 2 radios are close together and one xmits, the other squeals until theyre further apart. We all know that. My question is how does that happen with a repeater? If I xmit on 158.xxxx and Rx on 154.xxxx, how would the other radio still squeal if they are close if Im not using simplex? this happened to one of our firefighters using a mobile with his handheld on in the cab and I don't understand. Our radios I use at my full time job are on repeater also but they only pick up their voice when close to another and you get that echo effect but not the annoying squeal. Does it have to do with digital / analog or what?
 

12dbsinad

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I was curious about something and thought yall can help. When 2 radios are close together and one xmits, the other squeals until theyre further apart. We all know that. My question is how does that happen with a repeater? If I xmit on 158.xxxx and Rx on 154.xxxx, how would the other radio still squeal if they are close if Im not using simplex? this happened to one of our firefighters using a mobile with his handheld on in the cab and I don't understand. Our radios I use at my full time job are on repeater also but they only pick up their voice when close to another and you get that echo effect but not the annoying squeal. Does it have to do with digital / analog or what?
The repeater runs full duplex. Which means whatever is being transmitted on freq A you will hear on freq B at the same time. So essentially it is the same type of squeal as if you are on simplex. I would assume your work radios are digital? Fire on analog?
 
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Ramchops

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yes. our fire is analog and work is digital. Thanks for the info, but what is the benefit of running full duplex vs. whatever other options there may be? also essentially your saying were transmitting on both frequencies?
 

KG4INW

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It's the same principle, even on a repeated channel. The mic being used picks up received audio from the idle radio.
 

jim202

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It's the same principle, even on a repeated channel. The mic being used picks up received audio from the idle radio.

It's called feedback. Like was said before if you have 2 radios close together on a simplex channel, you can talk on one and hear yourself coming out of the other radio. If the volume is turned up loud enough on the radio receiving, you will get feedback and what you call the squeal.

The same thing can happen with the repeater. Only now your using a radio repeater that is some what removed from where the 2 portable radios are being used. Depending on the repeater and the audio control circuitry, there might be a slight delay or echo in the voice. But again, if the volume is turned up high enough on the portable doing the receiving, you can get the feedback.
 

12dbsinad

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yes. our fire is analog and work is digital. Thanks for the info, but what is the benefit of running full duplex vs. whatever other options there may be? also essentially your saying were transmitting on both frequencies?
A repeater is essetially used to increase range from handhelds and/or mobile units. When you transmit, it goes to the repeater, with a large antenna usually and at a nice high location to recieve your low power handheld. It then re-transmits (at the same time) on anouther frequency back out at a lot higher power level, to a handheld lets say way across a town or city, and vise versa. On simplex, talking portable to portable would never achieve this, unless you are relitively close to each other.
 

Ramchops

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A repeater is essetially used to increase range from handhelds and/or mobile units. When you transmit, it goes to the repeater, with a large antenna usually and at a nice high location to recieve your low power handheld. It then re-transmits (at the same time) on anouther frequency back out at a lot higher power level, to a handheld lets say way across a town or city, and vise versa. On simplex, talking portable to portable would never achieve this, unless you are relitively close to each other.
Thanks for the replies.... I understand what a repeater does, but I always thought (that's probably the problem) that if im out a ways from the repeater and transmit on one freq, I receive on the other, therefore I figured there should be no feedback like we get, but I suppose if were txing across both freqs that would make sense. Our work radios will not feedback a squeal at all, only the echo effect of the voice.
 

ramal121

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Yes it's audio feedback. Nothing to do with the RF path (simplex vs a repeater). If a microphone picks up its own audio it will pass it back through a loop. Without any delay (analog) this will settle out as a loud squeal usually around the higher end frequency of the audio passband. It won't go much higher because the passband starts dropping off and can't support feedback higher than the squeal your getting (which is annoying enough).

With digital there is a time delay on receive that prevents the feedback from getting up to the squeal frequencies, but instead gives the weird escalating echo thing.
 

gtaman

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When on a repeater I call this the whammie effect. The delay of the repeater cause the feedback to echo and be delayed. It happen on p25 digital in general on simplex because of the vocoder delay. It happens in analog too with a digital vocoder.
 
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